Spark plug



June 1l, 1957 R. c. TowNsEND, SR 2,795,723

SPARK PLUG Filed March 3, 1954 i INVENTOR Por C'. Wsw/www, f.

BY Q Q /,/,7Q,

ATTORNEY SPARK PLUG Roy C. Townsend, Sr., La Crosse, Wis.

Application March 3, 1954, Serial No. 413,792 2 claims. (cl. 313-141) This invention relates generally to .improvements in spark plugs for internal combustion engines and like uses, and more particularly relates to improvements in the igniter electrodes or points of such plugs.

As is commonly known the compressed, combustible fuel-air mixture in the cylinder of an engine is tired by the instantaneous impression of a high electrical potential across the electrodes of a spark plug, which causes a spark to jump the gap between the electrodes and ignite or kindle the mixture. The usual spark plug has a body made up of a rnetal shell 4threaded `to screw into the cylinder head and an Vinsulator through which connection is made to a center electrode from the ignitionsystem, the other side of the circuit being through ground (or rather through the engine and metal shell of the plug) from the latter of which an outer or second electrode projects into proximity to the center electrode. Obviously the electrodes and the innerpportions of the plug itself are exposed'to the gases in the combustion chamber sgo that the spark Vas it jumps between the electrodes will be exposed to the fuel-air mixture for igniting the same. The gap between the electrodes must be properly adjusted, this being 'an operation commonly called gapping Newly installed plugs in engines in good condition operate eiectively until sufficient wear occurs so that lubricant enters the combustion chamber and burns, forming a carbonaceous deposit upon the insulator. Initially the insulator, of course, has very high electrical resistance but as the insulator becomes fouled by the comparatively electrically conductive deposit of carbon formed upon it, its resistance is lowered and ignition becomes faulty, particularly when the engine is idling. The condition of the insulator also has a bearing upon the length or spacing of the gap between the electrodes and to prolong the useful life of the plug after its insulator resistance is lowered it is necessary to reduce the gap between the electrodes, although in presently used plugs this has a tendency to further shield the spark and make for poorer ignition. At all times, of course, the insulator resistance must exceed the spark gap resistance or there will be no spark.

All presently used spark plugs with which I am familiar employ electrodes having parallel surfaces defining the spark gap and by the very nature of the construction and arrangement of these electrodes they must be spaced at a considerable distance apart if the spark is not to be shielded from the combustible mixture in the cylinder and any attempt to reduce this spacing as the resistance of the insulators decrease due to fouling only results in an increased shielding of the spark to the point where ignition becomes exceedingly irregular, particularly when the engine is idling.

Having in mind the foregoing it is the primary object of my invention to provide an improved arrangement and construction for the electrodes of a spark plug which will permit the spark gap to be reduced as fouling of the insulator occurs without shielding the spark from the mixture. As a further object of my invention l provide a 2 spark gap arrangement in which the gap itself is of more than usual width so that there occurs what may be referred to as a ribbon of flame Aas the electrical potential arcs between the electrodes, thus furthermore to improve ignition. Still another object of my invention is to provide an arrangement wherein the outer electrode angles toward the face of the 'center electrode and lis also beveled off so that the spark must form at the extreme edge of the outer electrode to thereby obtain the maximum exposure of the llame to the mixture in the cylinder. j

These and other more detailed and specic objects will be disclosed in the course of the following specification, reference being had to the accompanying drawings, in which: l

Fig. l is a side elevation of a'spark plug with the lo'wer end in section,- embodying the electrodes or igniter points accordingfto my invention and showing the plug as associated with a cylinder head illustrated in dotted lines. Fig. 2 is an end view ofthe spark plug viewing the same at theend at which the electrodes are located.

Fig. V3 is Aan enlarged ldetail side elevation of the lower portion or" the insulator and adjacent portions of the electrodes, showing the manner in which the arc is formed between the endvof theouterelectrode and nearest adjacent surface `of the 'center electrode.

Fig. 4 is a view similar to Fig. 3 but taken at an angle of ninety degrees thereto to better illustrate the ribbonlike nature 'of the 'arc as it forms between the electrodes.

Referring now 4kmore particularly and' by reference characters to the 'drawing it will be noted that the 'spark plug as thereindisclosed is made up of the usual metallic outer shell, designated generally at'A, having a cylindrical threaded portion B so that it may be screwed intox the cylinder'head, ,indicated inv the dotted outlines C. The cylinde'rheadfQ, of course, defines a'combustio'n chamber, designated at D, at'the end "of a cylinder (not shown) and it will be htdthat fthe inner "or Alower endofrthe spark plug is exposed in the chamber so that the spark developed by the plug will ignite the compressed fuel-air mixture therein. Firmly held in the usual manner in the shell A is an insulator E of porcelain or some analogous material and upon the upper or outer end of the plug there is the usual terminal F for connection to the ignition system.

The lower end of the insulator E, designated at E', tapers in a downward direction within the cylindrical lower end B of the metallic shell of the plug and extending downwardly through the insulator within the terminal F is the usual electrical conductor G by which electrical connection is made to a center electrode 10 held rmly against the lower end of the insulator. This electrode 1d, commonly referred to as one of the points of the plug, is usually circular in shape as I have shown it in the drawings, but in accordance with my invention its diameter is considerably greater than the usual point. Cooperating with this center electrode 10 is an outer or second electrode, designated generally at 12, suitably secured at 13 to the end of the metallic shell A from which point the electrode extends radially inward toward the center axis of the plug. In the ordinary case the electrode l2 is also quite narrow but in accordance with my invention it is made of substantial width and preferably of approximately a width equaling the diameter of the center electrode 10, as clearly shown.

Furthermore, usual practice would call for the electrode 12 to extend straight across the center electrode 10 in a plane normal to the vertical axis through the plug so that, as described hereinbefore, the spark gap would be defined between two parallel and flat surfaces and would, therefore, be to a considerable extent shielded from the mixture in the chamber D.

trode 12 projects from the shell A ofthe plug for a sufcient distance so that when it is turned inward toward the center axis of the plug its inner end portion 14 appreaches; the center electrode atan angle. VThe Yextremity 15 of the inner end 0f electrodeY 12 terminates approximately on the center line of the plug and due to the angular relationship just described this extremity is the closest point between the two electrodes. In addition the extremity 15 is beveled olit as clearly shown so that there results in the formation of `a sharp edge, designated at 17 in Fig. 3, extending approximately the full width or diameter of the center electrode 10 and it is from this edge that the spark Wi'll` jump between the electrodes as a rectangular spark gap, the length of which is approximately equal to the diameter of sad'end face and Width of the outer electrode.

Not only do electrodes constructed in accordance with this invention provide the best possible ignition under ideal conditions, but they also extend the useful life of the spark plug after'the insulator thereof has become fouled by the deposit of carbon on it, for the reason that it is possible to reduce the gap between the electrodes with little, if any, reduction in the exposure of the spark to the fuel and air mixture in the combustion chamber. Furthermore, the construction is such that the usual point regapping tool (not shown) may be used as will be understood.

It is understood that suitable modifications may be made in the structure as disclosed, provided such modications come within the spirit and scope of the appended claims. Having now therefore fully illustrated and deafreyrasY K f 4 scribed my invention, what I claim to be new and desire to protect by Letters Patent is:

1. In a spark plug, improved igniter electrodes therefor comprising in combination a large diameter center electrode having a flat end face, an outer electrode of thin flat material having parallel sides and substantially equal in width to the diameter of said center electrode, the said outer electrode extending radially toward the center electrode and as viewed from theside of the plug approaching the center electrode at an angle toward the said end face thereof, the outer electrode having a beveled end with an acute-angled edge spaced from the end face of the center electrode and in conjunction with said end face forming a rectangularspark gap equal in length to the diameter of the center electrode and to the width of the outer electrode.

2. Spark plug igniter electrodes comprising in combination a center electrode of larger than usual diameter and having a dat end face, an outer electrode of thin at material having parallel sides and substantially equal in width to the diameter of said center electrode, the said outer electrode having a straight portion extending radially toward the center electrode and as viewed from the side of the plug approaching the center electrode at an angle ofrapproximately ten degrees to said end face thereof, the outer electrode being beveled crosswise at approximately forty-tive degrees and having an acute angled edge spaced from the end face of the center electrode and in conjunction with said end face forming a rectangular spark gap equal in length to the diameter of the center electrode and Width of the outer electrode.

References Cited in the le of this patent UNITED STATES PATENTS 1,538,870 Champion May 19, 1925 1,942,242 Fitzgerald Jan. 2, 1934 1,968,225 Shell Iuly 31, 1934 2,518,844 Wetzel Aug. 15, 1950 FOREIGN PATENTS 399,086 Germany Mar. 18, 1923 

